Acid zinc electroplating

ABSTRACT

R&#39;&#39;&#39;&#39; is an alkyl group of one to four carbon atoms; and X is a halide ion; and B. A WATER-SOLUBLE CONDENSATION PRODUCT OF A BENZENE OR NAPHTHALENE SULFONIC ACID, OR SALT THEREOF, WITH FORMALDEHYDE, SAID CONDENSATION PRODUCT CONTAINING AT LEAST 2 BENZENE OR NAPHTHALENE SULFONIC ACID GROUPS CONNECTED WITH EACH OTHER BY METHYLENE BRIDGES.   WHEREIN R is -CONH2, -CN, -CHO or -COOR&#39;&#39;&#39;&#39;; R&#39;&#39; is an alkyl group of one to four carbon atoms, -CH2CH CH2, CH2O*CH, -CH2CH CHCH2X, -CH2COOR&#39;&#39;&#39;&#39; or   Acid zinc electroplating baths at pH 3.5 to 7.5 are provided which have dissolved therein as additives A. A PYRIDINIUM COMPOUND OF THE GENERAL FORMULA:

United States Patent 0 1 Rushmere Oct. 30, 1973 ACID ZINC ELECTROPLATING [75] Inventor: John DerekRushmere, Wilmington,

Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

22 Filed: May 23, 1972 21 Appl. No.: 256,179

52 us. Cl. 204/55 R 51 Int. Cl. C23b 5/12, C23b 5-/46 53 Field of Search 204/55 v, 55 R, 432,

[56] References Cited UNITED STATES PATENTS- 5/1967 Rindt et a]. 204/55 Y 11/1968 Rushmere 204/55 -Y X Primary ExaminerG. L. Kaplan Attorney-Robert W. Black [57] ABSTRACT Acid zinc electroplating baths at pH 3.5 to 7.5 are provided which have dissolved therein as additives a. a pyridinium compound of the general formula:

wherein R is CONH,, -CN, CHO or COOR; R is an alkyl group of one to four carbon atoms, CH,CH=CH,, CH,O CH, CH,CH=CHCH,X, --CH,COOR" or 15 Claims, N0 Drawings BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates to acid zinc electroplating baths and processes, and additives useful therein, and, more particularly, to such baths and processes for depositing bright zinc plates.

2. Prior Art Numerous patents concerned with bright zinc deposits obtained from acid zinc baths have issued over the years. U.S. Pat. No. 3,537,959 issued Nov. 3, 1970, to Joachim Korpiun and Hans J. Steeg, is directed to the co-use of primary amines and naphthalene sulfonic acid-formaldehyde condensation products for this purpose. The co-use of quaternized pyridines with linear polyethers for acid zinc plating is disclosed in German Pat. No. 2,111,602 published Mar. 18, 1970My copending application Ser. No. 157,662, filed June 28, 1971, discloses the use of certain quaternized pyridine compounds in acid zinc plating. Other patents directed to the use of sulfur and nitrogen compounds include U.S. Pat. No. 2,355,505 issued to John L. Bray and Robert E. Howard on Aug. 8, 1944, and U.S. Pat. No. 2,543,545, issued to Charles L. Faust and Arthur E. Bearse on Feb. 27, 1951, which discloses the use of sulfonated heterocyclics.

Quaternary pyridine compound additives useful in alkaline cyanide zinc plating are described in U.S. Pat. No. 3,318,787 issued to Gustav Rindt and Donald H. Becking on May 9, 1967, and certain pyridinium compounds useful in alkaline zinc plating are described in U.S. Pat. No. 3,411,996, issued to John D. Rushmere on Nov. 19, 1968.

SUMMARY OF THE INVENTION According to the present invention there is provided an aqueous acid zinc electroplating bath comprising an aqueous solution of zinc ions, said solution maintained at a pH in the range of about 3.5 and 7.5 and having dissolved therein in an amount effective to give a bright zinc deposit, (a) a pyridinium compound of the general formula:

wherein a is -coNH,, -CN, CHO or COOR"; I R is an alkyl group of one to four carbon atoms, -CH CH=CH -CI-l C WW CH, CH CH=CHCH X, CH COOR" or R" is an alkyl group of one to four carbon atoms; and

X'is a halide ion; and

b. a water-soluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof, with formaldehyde, said condensation product containing at least 2 benzene or naphthalene sulfonic acid groups connected with each other by methylene bridges.

Also provided is a process of electroplating bright zinc using the above acid zinc electroplating bath.

There is also provided an aqueous addition agent for a zinc electroplating bath consisting essentially of an aqueous solution with about 1 to 25 percent by weight of the above-described pyridinium compound and about 1 to 50 percent by weight of the above-described condensation product.

DETAILED DESCRIPTION OF THE INVENTION This invention pertains to the electrodeposition of zinc from acid zinc plating baths known to those skilled in the art. These baths may be formed by the dissolution of zinc oxide in common industrial acids such as hydrochloric, sulfuric, sulfamic and fluoboric. More commonly, however, the baths are formed by the dissolution of commercial zinc and ammonium salts such as the sulfates, chlorides, acetates, fluoborates or sulfamates in water with subsequent adjustment of pH to the normal or desired range by means of aqueous ammonia, ammonium hydroxide or other bases, or an acid as required.

While the bath pH will generally be at a slightly acidic pH between 3.5 and 6, a higher pH bath, such as to pH 7.5, may be used, by the addition of a base such as ammonium hydroxide. However, for this invention,

it is preferred to operate at a pH between 5 and 6 when using the preferred zinc chloride bath.

In such a zinc chloride bath, ammonium chloride is added to improve electrical conductivity. Also, the bath will have a chloride ion to zinc ion weight ratio in the range from 4/1 to 16/ l preferably from 6/1 to 12/ 1. Zinc metal content in the zinc chloride bath, as well as the other acid 'zinc baths, will range from about 6 to 45 grams per liter, preferably about 6 to 20 grams per liter.

Bath formulations may contain mixtures of zinc salts such as the use of both zinc chloride and zinc sulfate. However, there appears to be little practical advantage for doing this. Bath formulations may also contain other metal salts such as a conductivity increasing salt, like sodium sulfamate or potassium sulfate.

Zinc deposits of acceptable commercial quality can be obtained from a bath operated at a temperature 'in the range of about 10 to 45C. Normally, the bath is operated at about 20 to 30C.

Zinc deposits obtained from such acid baths are typically coarse and dull gray in appearance and have little commercial value, especially in decorative plating of screws, chains and other items of hardware. It has now been found that when an additive combination comprising a mixture of certain quaternized pyridine compounds and water-soluble condensation products of an aryl sulfonic acid with formaldehyde is added to the acid z'inc bath, bright, shiny zinc of high decorative quality can be obtained from both barrel plating and rack plating operations. The pyridinium compounds useful in the present invention have the general formula:

wherein R" is an alkyl group of one to four carbon atoms;

R is CONH -CN, Cl-l or COOR; and

X is a halogen selected from fluorine, chlorine and bromine. The pyridinium compound is used at a concentration level of about 0.02 to 20 grams per liter, preferably about 0.05 to grams per liter.

Preferred pyridinium compounds are l-allyl, 3- carbox-amido pyridinium halide where the halide is chloride, bromide or iodide. Other compounds that have been found useful include:

l. l-methyl, 3-carboxamido pyridinium bromide.

2. l-propargyl, 3-carboxamido pyridinium bromide.

3. l-(4-chlorobutene-2), 3-carboxamido pyridinium chloride.

4. 2-butene 1,4 bis( 3-carboxamido pyridinium chloride).

5. l-carbomethoxymethyl, 3-carboxamido pyridinium chloride.

6. l-propargyl, 3-carbomethoxy pyridinium bromide.

7. l-allyl, 3-cyano pyridinium bromide.

8. l-allyl, 3-formyl pyridinium bromide.

The second component of the additive is a watersoluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof (usually alkali metal), with formaldehyde containing at least two benzene or naphthalene sulfonic acid groups which are connected with each other by means of methylene bridges. A naphthalene sulfonic acid is preferred. Preparation of these products is known and one such method is mentioned in US. Pat. No. 3,537,959. The condensation product is added in an amount to give a bath concentration of about 0.5 to 50 grams per liter, preferably about t to 20 grams per liter. The particular concentration used and found effective will depend upon the type and amount of pyridinium compound used and whether rack or barrel plating is being used.

The brightener combination of the present invention is preferably and effectively used as an aqueous solution addition agent containing about 1 to 25 percent by weight, preferably about -1 to percent, of the pyridinium compound and about i to 50 percent by weight, preferably about 1 to 20 percent, of the condensation product. A particularly effective addition agent uses l-allyl, 3-carboxamido pyridinium chloride as the pyridinium compound and the sodium salt of a naphthalene sulfonic acid-formaldehyde condensation product. The addition agent is normally used by adding about 5 to 20 ml. of solution per liter of bath although larger amounts (such as up to 50 ml./l. can be used with effectiveness).

The invention can be further understood by referring to the examples in which parts and percentages are by weight unless otherwise indicated.

In conducting the following examples, a basic zinc chloride bath containing:

was used unless otherwise noted. Temperature of operation was 2228C. again unless otherwise noted.

EXAMPLE 1 A steel Hull Cell panel was plated at 2 amps for 5 minutes in the basic bath containing 2.0 g./l. of a waters'oluble condensation product between naphthalene sulfonic acid and formaldehyde (Darvan No. 1) and 0.8 g./l. l-methyl, 3-carboxamido pyridinium bromide. Bright plate was obtained over the current density range 8-80 amps/ft. Some pitting of the deposit occurred.

EXAMPLE 2 A steel Hull Cell panel was plated at 2 amps for 5 minutes in the basic bath containing 2.0 g./l. Darvan No. l and 2.0 g./l. l-propargyl, 3-carboxamido pyridinium bromide. Very bright plate free of pits was obtained over the current density range 2-60 amps/ft.

EXAMPLE 3 EXAMPLE 4 30 g. No. 6 X 7% inch steel wood screws were barrel plated in a minibarrel at 2 amps for 20 minutes in the basic bath containing 2.0 g./l. Darvan No. l and 0.4 g./l. l-allyl, 3-car boxamido pyridinium bromide. A very bright lustrous zinc deposit was obtained. The deposit took both a nitric acid bright dip and a chromate con version dip without difficulty.

EXAMPLE 5 A 30 g. load of No. 6 X 12 inch steel wood screws was barrel plated at 2 amps for 20 minutes in the basic bath containing 1.0 g./l. of a water-soluble condensation product between benzene sulfonic acid and formalde- EXAMPLES 6-1 1 Minibarrel plating tests were conducted on 30 g. loads of screws, plated at 2 amps for 20 minutes, using the basic zinc chloride bath to which had been added 2.0 g./l. Daxad No. ll. In addition, quaternized pyridines were added in the amounts stated and with the results shown in Table l.

after bright clip. I Dark color. S-carboxamido pyridinium bromide l-carbomethoxy 2 Shiny bright product rs r L after bright dip.

3-carboxamido pyridinium bromide EXAMPLE 12 The pH of the basic zinc chloride bath was raised to pH 7.2 by the addition of ammonia. 30 g. of screws were then plated at 2 amps for minutes using this bath to which had been added 2.0 g./l. Darvan No. l and 0.8 g./l. l-allyl, 3-carboxamido pyridinium bromide. After bright dipping, the screws were bright and shiny; however, they lacked the liquid brightness of screws plated at lower pH from this bath.

EXAMPLE 13 To a zinc sulfate bath containing:

250 g./l. ZnSO -7H O 30 g./l. (Ni-[0 80 pH 3.8 v was added as brightener 2.0 g./l. Darvan No. 1 and 0.8 g./l. l-allyl 3-carboxamido pyridinium bromide. 30 g. of screws were barrel plated at 2 amps for 20 minutes in a minibarrel using this bath. As plated they were semibright. After dipping in 0.5 weight percent nitric acid, brightness was improved and they were of acceptable commercial quality.

EXAMPLE 14 A 4-liter basic basic zinc chloride bath was operated for 610 ampere hours of barrel plating electrolysis using a 10 percent by weight aqueous brightener containing parts of a water-soluble condensation product between naphthalene sulfonic acid and formaldehyde and 1 part of l-allyl, 3-carboxamido pyridinium chloride. Average temperature of operation was 20-25C. and the bath was producing fully bright zinc deposits. Temperature of the bath was raised successively to C., C., C. and C. As the temperature was raised, some brightness was lost from the deposit, more particularly the liquid luster. However, work of acceptable commercial quality was obtained, after bright dipping, even at 45C.

What is claimed is:

6 1. An aqueous acid zinc electroplating bath comprising an aqueous solution of zinc ions, said solution maintained at a pH in the range of about 3.5 to 7.5, and having dissolved therein in an amount effective to give a bright zinc'deposit, (a) a pyridinium compound of the general formula:

., .mmc ,7

wherein R is an alkyl group of one to four carbon atoms, CH CH=C H CI-l C E CH,

R" is an alkyl group of one to four carbon atoms;

X is a halogen selected from iodine, chlorine and bromine; and b. a water-soluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof, with formaldehyde, said condensation product containing at least 2 benzene or naphthalene sulfonic acid groups connected with each other by methylene bridges.

2. The acid electroplating bath of claim 1 wherein the pyridinium compound is present in an amount in the range of about 0.02 to 20 grams per liter and the condensation product is present in an amount of about 0.5 to grams per liter.

3. The acid electroplating bath of claim 2 wherein the pyridinium compound is selected from the group consisting of l-allyl, 3-carboxamido pyridinium halide; 1- methyl, 3-carboxamido pyridinium halide; l-propargyl, 3-carboxamido pyridinium halide; l-(4-chlorobutene- 2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3-carboxami'clo pyridinium halide); l-carbomethoxymethyl, 3-carboxamido pyridinium halide; lpropargyl, Zi-carbomethoxy pyridinium halide; l-allyl, 3-cyano pyridinium halide and l-allyl, 3-formyl pyridinium halide.

4. The acid electroplating bath of claim 3 wherein the pH of the bath is within the range of about 5 to 6.

5. The acid electroplating bath of claim 4 wherein the pyridinium compound is present in an amount in the range of about 0.05 to 5 grams per liter and the condensation product is present in an amount in the range of about 1 to 20 grams per liter.

6. The'acid electroplating bath of claim 5 wherein the pyridinium compound is l-allyl 3-carboxamido pyridinium halide and the sulfonic acid used in the condensationproduct is naphthalene sulfonic acid.

7. The acid electroplating bath of claim 4 wherein the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 4 0 grams per liter and having a chloride ion to zinc ion carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and (b) about 1 to 20 grams per liter of a water-soluble condensation product of a naphthalene sulfonic acid with formaldehyde, said condensation product containing at least two naphthalene sulfonic acid groups connected with each other by methylene bridges.

9. in a process of electroplating bright zinc from an aqueous acid zinc electroplating bath having zinc ions dissolved therein the improvement comprising: main-,

taining the bath at a pH in the range of about 3.5 to 7.5 and adding thereto in an amount effective to give a bright zinc deposit (a) a pyridinium compound of the general formula:

wherein R is an alkyl group of one to four carbon atoms, 1

R"is an alkyl group of one to four carbon atoms; R is CONH -CN, CHO or COOR";

X is a halogen selected from iodine, chlorine and brorange of about 0.02 to 20 grams per liter and the condensation product is added to give a bath concentration in the range of about 0.5 to 50 grams per liter.

11. The process of claim 10 wherein the pyridinium compound is selected from the group consisting of lallyl, 3-carboxamido pyridinium halide; l-methyl, 3- carboxamido pyridinium halide; l-propargyl, 3- carboxamido pyridinium'halide; l-(4-chlorobutene-2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3- carboxamido pyridinium halide); l-carbomethoxymethyl, 3-carboxamido pyridinium halide; lpropargyl, 3-carbomethoxy pyridinium halide; l-allyl, S-cyano pyridinium halide and l-allyl, 3-formyl pyridinium halide.

12. The process of claim 11 wherein the pH of the bath is within the range of about 5 to 6, the pyridinium compound is added to give a concentration in the range of about 0.05 to 5 grams per liter and the condensation product is added to give a concentration in the range of about 1 to 20 grams per liter.

13. The process of claim 12 wherein the bath is operated at a temperature in the range of about 10 to 45C.

14. The process of claim 12 wherein the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 grams per liter and having a chloride ion to zinc ion weight ratio in the range of about 4/ 1 to 16/1.

15. in a process of electroplating bright zinc from an aqueous acidzinc chloride electroplating bath containing zinc ions dissolved therein at a concentration in the range of about 6 to 20 grams per liter and having a chloride ion to zinc ion weight ratio within the range of about 6/1 to 12/ l, the improvement comprising: maintaining the bath at a pH in the range of about 5 to 6 and the temperature in the range of about 20 to 30C. and adding thereto (a) about 0.05 to 5 grams per liter of lallyl, 3-carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and (b) about 1 to 20 grams per liter of a water-soluble condensation product of a naphthalene sulfonic acid with formaldehyde, said condensation product containing at least two naphthalene sulfonic acid groups connected with each other by methylene bridges. 

2. The acid electroplating bath of claim 1 wherein the pyridinium compound is present in an amount in the range of about 0.02 to 20 grams per liter and the condensation product is present in an amount of about 0.5 to 50 grams per liter.
 3. The acid electroplating bath of claim 2 wherein the pyridinium compound is selected from the group consisting of 1-allyl, 3-carboxamido pyridinium halide; 1-methyl, 3-carboxamido pyridinium halide; 1-propargyl, 3-carboxamido pyridinium halide; 1-(4-chlorobutene-2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3-carboxamido pyridinium halide); 1-carbomethoxymethyl, 3-carboxamido pyridinium halide; 1-propargyl, 3-carbomethoxy pyridinium halide; 1-allyl, 3-cyano pyridinium halide and 1-allyl, 3-formyl pyridinium halide.
 4. The acid electroplating bath of claim 3 wherein the pH of the bath is within the range of about 5 to
 6. 5. The acid electroplating bath of claim 4 wherein the pyridinium compound is present in an amount in the range of about 0.05 to 5 grams per liter and the condensation product is present in an amount in the range of about 1 to 20 grams per liter.
 6. The acid electroplating bath of claim 5 wherein the pyridinium compound is 1-allyl 3-carboxamido pyridinium halide and the sulfonic acid used in the condensation product is naphthalene sulfonic acid.
 7. The acid electroplating bath of claim 4 wherein the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 grams per liter and having a chloride ion to zinc ion weight ratio in the range of about 4/1 to 16/1.
 8. An aqueous acid zinc chloride electroplating bath comprising an aqueous solution of zinc ions at a concentration in the range of about 6 to 20 grams per liter and having a chloride ion to zinc ion weight ratio within the range of about 6/1 to 12/1, said solution maintained at a pH of about 5 to 6 and having dissolved therein (a) about 0.05 to 5 grams per liter of 1-allyl, 3-carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and (b) about 1 to 20 grams per liter of a water-soluble condensation product of a naphthalene sulfonic acid with formaldehyde, said Condensation product containing at least two naphthalene sulfonic acid groups connected with each other by methylene bridges.
 9. In a process of electroplating bright zinc from an aqueous acid zinc electroplating bath having zinc ions dissolved therein the improvement comprising: maintaining the bath at a pH in the range of about 3.5 to 7.5 and adding thereto in an amount effective to give a bright zinc deposit (a) a pyridinium compound of the general formula:
 10. The process of claim 9 wherein the pyridinium compound is added to give a bath concentration in the range of about 0.02 to 20 grams per liter and the condensation product is added to give a bath concentration in the range of about 0.5 to 50 grams per liter.
 11. The process of claim 10 wherein the pyridinium compound is selected from the group consisting of 1-allyl, 3-carboxamido pyridinium halide; 1-methyl, 3-carboxamido pyridinium halide; 1-propargyl, 3-carboxamido pyridinium halide; 1-(4-chlorobutene-2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3-carboxamido pyridinium halide); 1-carbomethoxymethyl, 3-carboxamido pyridinium halide; 1-propargyl, 3-carbomethoxy pyridinium halide; 1-allyl, 3-cyano pyridinium halide and 1-allyl, 3-formyl pyridinium halide.
 12. The process of claim 11 wherein the pH of the bath is within the range of about 5 to 6, the pyridinium compound is added to give a concentration in the range of about 0.05 to 5 grams per liter and the condensation product is added to give a concentration in the range of about 1 to 20 grams per liter.
 13. The process of claim 12 wherein the bath is operated at a temperature in the range of about 10* to 45*C.
 14. The process of claim 12 wherein the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 grams per liter and having a chloride ion to zinc ion weight ratio in the range of about 4/1 to 16/1.
 15. In a process of electroplating bright zinc from an aqueous acid zinc chloride electroplating bath containing zinc ions dissolved therein at a concentration in the range of about 6 to 20 grams per liter and having a chloride ion to zinc ion weight ratio within the range of about 6/1 to 12/1, the improvement comprising: maintaining the bath at a pH in the range of about 5 to 6 and the temperature in the range of about 20* to 30*C. and adding thereto (a) about 0.05 to 5 grams per liter of 1-allyl, 3-carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and (b) about 1 to 20 grams per liter of a water-soluble condensation product of a naphthalene sulfonic acid with formaldehyde, said condensation product containing at least two naphthalene sulfonic acid groups connected with each other by methylene bridges. 